1. Field of the Invention
The subject invention relates to methods and apparatus for conditioning batteries, including secondary batteries, for their electric energy or current supplying operation or for an electric potential providing function. The subject invention relates also to methods and apparatus for utilizing batteries to their full capacity, and for minimizing such drawbacks as unwanted memory pheonomena, cell reversal, the lack of an external test for determining state of charge, and other deficiencies of certain secondary batteries.
2. Disclosure Statement
This disclosure statement is made pursuant to the duty of disclosure imposed by law and formulated in 37 CFR 1.56(a). No representation is hereby made that information thus disclosed in fact constitutes prior art inasmuch as 37 CFR 1.56(a) relies on a materiality concept which depends on uncertain and inevitably subjective elements of substantial likelihood and reasonableness, and inasmuch as a growing attitude appears to require citation of material which might lead to a discovery of pertinent material through not necessarily being of itself pertinent.
It is well known that the state of charge of an electric battery cannot reliably be determined by a mere measurement of the battery voltage. According to a widespread practice, the specific gravity of the sulfuric acid electrolyte is measured in the case of liquid-electrolyte lead-acid batteries in order to gain information about the charge condition of the battery. Even though this method requires an inconvenient and hazardous manipulation of the acid electrolyte, the lack of a competitive better solution has perpetuated its practice.
Moreover, even that inconvenient and harzardous technique is unavailable in the case of sealed batteries and in the case of all nickel-cadmium cells and other batteries where the electrolyte is either inacessible or does not by its specific gravity indicate the level of charge of the battery. Apart from the fact that there is no external test which will indicate the state of charge for most battery types, it is also a familiar observation that conventional trickle and standby charging methods have uncertain effects on batteries. In fact, many nickel-cadmium battery and other rechargeable cell types suffer frequently unexplained losses of charging capacity commonly attributed to internal electrochemical phenomena.
Reference may in this respect be had to the article by Pensabene and Gould, entitled "Unwanted Memory Spooks Nickel-cadmium Cells" (IEEE Spectrum, Sept. 1976), pp. 33 to 36. While that article addresses itself to nickel-cadmium cells, it does describe various undesirable phenomena known with various types of secondary cells, including a detrimental memory effect diminishing charging capacity, a loss of contact between electron conductors, impregnated active chemicals, and the electrolyte, cell reversal and other disturbances in the battery's electrochemistry.
To alleviate these problems, there have been suggestions in the past that a secondary battery should simply be discharged from time to time to rid the battery of unexplained losses in charging capacity. Such arbitrary discharging is not only of questionable value as far as correction of electrochemical phenomena is concerned, but may in effect damage or destroy the battery, particularly in the case of batteries which suffer from a discharged state or from the heat generated by uncontrolled discharge.
Conversely, many battery charging methods expose batteries to a damaging overcharge.